This application is based on French Patent Application No. 01 02 805 filed Mar. 1, 2001, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. xc2xa7119.
1. Field of the Invention
The invention relates to a cellular mobile telephone system that can be used on board a vehicle, such as an aircraft, a train, a ship, etc., and which uses a satellite link.
2. Description of the Prior Art
The document WO 94/28684 describes a cellular mobile telephone system that can be used on board an aircraft. It enables conventional GSM mobile telephones to be used by connecting them to GSM base transceiver stations on board the aircraft by means of cables or infrared links, in order to prevent all risk of radio waves emitted by the mobile telephones interfering with navigation equipment. The base transceiver stations are connected to a base station controller which is also on board the aircraft and connected to an onboard switch. The onboard controller is connected to a terrestrial mobile telephone network by a direct radio link or via a satellite.
The document WO 98/21838 describes a system which is similar except that it includes a base station controller and a switch that are on the ground instead of on board the aircraft. An onboard base transceiver station is connected to the base station controller by a satellite link.
The document EP 0.998.062 describes a cellular mobile telephone system that can be used on board an aircraft. It enables conventional GSM mobile telephones to be used in the conventional way, i.e. with no cable or infrared link to connect them to onboard GSM base transceiver stations. The base transceiver stations are connected to an onboard controller which is connected to a terrestrial mobile telephone network by a satellite link.
The above prior art systems apply the standard GSM procedures. A signaling link must be set up first for an onboard mobile telephone to be able to perform an operation to enable the network to determine its location or to set up a call or for the terrestrial mobile network to set up a call to the aircraft. The GSM procedure for setting up a signaling link involves exchanging various signals. If a terrestrial digital telephone network executes the procedure, the time-delay on setting up the signaling link is imperceptible for users. If the signals are exchanged via a satellite system, the time-delay is several seconds (up to 20 seconds). This is a problem for users (who hang up because they believe the call has been lost) and for the telecommunication system itself (safety time-outs expire before the link is set up, aborting link set-up attempts).
The object of the invention is to propose a system that does not have this drawback of the prior art systems.
The invention consists in a cellular mobile telephone system that can be used on board an aircraft, the system including:
a first transceiver on board the vehicle and connected to an antenna outside the vehicle to set up an external radio link between the vehicle and a terrestrial mobile telephone network via a satellite; and
means in the vehicle for coupling mobile telephones inside the vehicle to the transceiver, which coupling means include means for setting up a permanent signaling link between the vehicle and the terrestrial mobile telephone network as soon as at least one mobile telephone is switched on.
The above system anticipates the requirement for a signaling link in that a permanent signaling link is set up as soon as a first mobile telephone is switched on and executes the procedure for determining its location. There is therefore never any delay caused by setting up a signaling link, with the possible exception of the first call set-up request, if the latter immediately follows switching on the first mobile telephone.
In the event of a small number of simultaneous call set-up requests, the requesting mobile telephones use the same signaling link successively, with no perceptible waiting time. If the number of simultaneous requests exceeds a predetermined number, a second signaling link is set in advance.
The invention will be better understood and other features will become apparent on reading the following description which is given with reference to the single figure of the accompanying drawing.